The first phase of our research program has been to develop the methods and materials to study the folate binding proteins in normal and abnormal folate metabolism. To this purpose we have isolated and characterized FABP from human and goat milk, purified FABP from various sera and placenta, produced mono-specific antibody to FABP, developed systems to study the effect of FABP on cellular uptake and metabolism and developed radioassays to measure total folate, bound folate, free folate, oxidized folate, red cell folate, total FABP, unsaturated FABP, and saturated FABP. The logical extension of this work is to (1) understand FABP function by utilizing these materials and assays for the study of previously unmeasured parameters of folate metabolism in the serum of patients with various clinical disorders and in other tissues such as milk, intestinal secretions, cerebrospinal fluid, leukocyte lysates, and homogenates of liver, kidney and placenta; (2) further evaluating the role of FABP in the cellular uptake of folates with particular attention to the membrane; (3) determining whether FABP influences the cellular distribution and metabolic function of folyl mono- and polyglutamates; (4) determining whether FABP influences the intestinal uptakes of the various folates in the normal or in patients with tropical sprue; (5) attempting the characterization of the large molecular weight FABP; (6) isolating additional FABP which preferentially binds reduced folates; (7) studying the effect of FABP on the clearance and tissue distribution of various folates and (8) further defining the binding site and mechanics of binding of various folates and anti-folates to FABP.